rollup.js is a module bundler for JavaScript. It compiles small piece of JavaScript modules spreading in different files into a single larger standardized ES code file. This post will show some entry level usage for this library.IntroductionNormally a bundler tool would compile a few small JavaScript files into a single JavaScript so that web browser can read, parse and render it properly. A bundler tool may be needed because of a few reasons:Some early stage browsers don't understand modules, the modularized JS codes need to be packed into standard JS code so that browser can understandThe mo...